1. Field of the Invention
The present invention relates to a pneumatic tire, more particularly to a bead structure suitable for heavy duty tires capable of improving bead durability.
2. Description of the Related Art
In general, heavy duty tires such as truck/bus tires are inflated to a very high pressure of 600 to 800 kPa.
Such heavy duty tires are disclosed in Japanese patent No. 3441720 and U.S. Pat. No. 6,736,177 cognate thereto, wherein a steel cord carcass ply (b) is secured to bead cores (c) in the bead portions by winding the ply edges (b2) around the bead cores as shown in FIG. 6.
In the bead portions of such a tire, due to the high inflation pressure and the application of a heavy tire load, the carcass ply main portion (b1) is pulled radially outwards, a force to rotate the bead core (c) occurs. As a result, the carcass cords are moved, and following the carcass ply the bead wire making up the core (c) is moved and the bead core is deformed. Further, the bead toe (Bt) is lifted from the bead seat (Js) of the rim (J). Such a deformed state is very liable to remain after freed from the pulling force. Thus, if the tire is once removed from the rim, it is difficult to remount the tire on the rim because a high percentage of the air injected into the tire to inflate the tire and to place the bead portions in place leaks through between the bead bottom and bead seat. Further, if well remounted, there is a possibility of bead unseating under very severe service conditions and deterioration of durability.